Question 508801
a = number of adults
400a = sales of adult tickets in cents (I'm using cents to avoid the decimals later)
c = number of children
150c = sales of children's tickets in cents
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a + c = 2200
so
a = 2200 -c
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400a + 150c = 505000 cents
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substitute
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400(2200-c) + 150c = 505000
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880000 -400c + 150c 505000
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-250c = -375000
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c = 1500
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a = 2200-c
a = 700
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check the receipts to see if this is correct
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4*700 = 2800
1.50*1500 = 2250
2800 + 2250 = 5050
correct
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Answer: They sold 700 adult and 1500 children tickets.
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Done.